Okay all, just putting this here to help those who may have this fault in the future. Warning long read ahead most likely. Wife's 2010 x35d has been exhibiting a trans fault (4F85) on very rare occasions. Happened three times at highway speeds over 6 months under very specific circumstances. Under passing requiring gear to drop and then letting off. All three times it trans failsafed (a good thing) and we coasted to a stop on the shoulder. Restart and drive home as normal.
Well, the last time (early January) was the last time for me. It has to be fixed. So I take it off the road throw it on jackstands and do some research (a lot of research). Now, the E clutch is engaged as a sort of assist clutch for 4,5, and 6. So 1-3 gear will operate fine. Now, the ZF6hp28 that is in the diesel is very similar to all the 6hp models so most of this will apply to all of those as well (the 19, 26, etc). Here is the best information I could find regarding the E clutch trans code.
https://axleaddict.com/auto-repair/Z...E-Clutch-Fault
This is the most dis-heartening quote in the article:
Quote:
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It’s an unfortunate fact that it’s almost impossible to diagnose the cause of the E clutch fault with 100% certainty... Clues can point you in the right direction, but practically speaking you might be as well just closing your eyes, pulling one of the possible causes out of a hat
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The TLDR of that article is that the cause could be a great many things. Some easy, some not so easy. Most are expensive. So I was going to work in a comprehensive manner and do all the things I could that did not require the trans being pulled. That included: oil pan/filter, mechatronic sleeve, 4 tube seals, bridge seal, and a valve body rebuild. Total for all this was ~$1000. My thinking is, I don't want to go in there more than once and if one of those was not the issue, the trans would have to come down anyway.
By the way, the valve body guys did warn me before purchasing that the probable cause would end up being the E clutch bushing that is referred to in that article. They were great and turnaround was crazy. Like 2 days. Highly recommend
Worldwide Specialty Parts out of Ohio. Was awesome of them to warn me prior to purchasing.
Here is my fluid after I dropped the old pan. Fluid did not smell burnt or overly bad. Lots of glitter/sparkles, but no worse than the 182000 mile E61 I just did with the 6hp19 in it so that didn't overly worry me. That 5er wagon shifts great now and is a joy to drive.
And the valve body in the car and then removed with the TCM taken off.
So I get the valve body back from them, again, crazy fast.
I reinstall the TCM, install the new tube and bridge seals, put the valve body back into the trans, new mechatronic sleeve, pan, and fill with fluid everything torqued to spec). 3.5ltrs first fill, start engine, warm up trans to 80F, added 3.5ltrs more, shifted trans through gears, warmed up to 104F, added 1.5ltrs more and got a trickle out and put the new drain plug in. All went just like the E61 in terms of fill. So I was unconcerned. Did a Xfer case fluid change because I was there and was tired of getting the expired fluid code every time I scanned the truck. Put the shields back on and took it off the jack stands. Then reset the Xfer case fluid values and code and cleared the transmission adaptations. Checked the tire air pressures (all low by 5-8psi from sitting) and set off on the test drive.
The 1-3 shifting is a little "hunty" but I expected that as after you clear the trans adaptations it shifts a little oddly for a 100 miles ish. That was the experience on my E61 and what I found in my research online as well. So I was stoked. Then I turn out of my neighborhood and the first time (and every subsequent time) the trans attempts to go into 4th gear I now get trans fail safe.
Clear the trans codes and after the 3rd time it failed going into 4th I just limped it back home and pulled it back into the garage, deflated. The codes now are 4F89 for 3-4 gear ratio monitoring. Not surprising as 4th is the first gear that uses the E clutch.
So, my last "hail mary" to try and avoid a full rebuild is going to be to fill the trans with Valvoline Maxlife multivehile ATF. It's a much thicker fluid and is a cheap attempt and I have seen some really good reviews about how it can bring ZF boxes back from the dead. Don't get me wrong, I'm not holding my breath. But for $40 worth of fluid it's worth a shot to attempt. I will update this thread with how I get on with it. I figure this will help someone. Let me know if you have any thoughts, opinions, condolences.
The patient:
